diff --git a/pcapkit/protocols/internet/ipv4.py b/pcapkit/protocols/internet/ipv4.py
index 511996f78a..296d3729f9 100644
--- a/pcapkit/protocols/internet/ipv4.py
+++ b/pcapkit/protocols/internet/ipv4.py
@@ -887,7 +887,8 @@ def _read_opt_sec(self, schema: 'Schema_SECOption', *, options: 'Option') -> 'Da
                     warn(f'{self.alias}: [OptNo {schema.type}] invalid format: remaining data', ProtocolWarning)
 
             if schema.data[-1] & 0x01 == 1:
-                warn(f'{self.alias}: [OptNo {schema.type}] invalid format: field termination indicator not set', ProtocolWarning)
+                warn(f'{self.alias}: [OptNo {schema.type}] invalid format: '
+                     f'field termination indicator set on the final octet: {schema.data[-1]!r}', ProtocolWarning)
             termination = tuple(bool(byte & 0x01) for byte in schema.data)
         else:
             flags = []
diff --git a/tests/protocols/internet/test_ipv4_roundtrip_unit.py b/tests/protocols/internet/test_ipv4_roundtrip_unit.py
index d8f1a952d7..ea4050fc32 100644
--- a/tests/protocols/internet/test_ipv4_roundtrip_unit.py
+++ b/tests/protocols/internet/test_ipv4_roundtrip_unit.py
@@ -156,9 +156,13 @@ def test_sec_termination_indicator_follows_rfc_1108(self) -> None:
             option = self.parse(header('8204ab90')).info.options[OptionNumber.SEC]
         self.assertEqual(option.flags, (ProtectionAuthority.GENSER, ProtectionAuthority.NSA))
 
-        # The low-order bit set on the final octet promises another octet.
-        with self.assertWarnsRegex(ProtocolWarning, 'field termination indicator not set'):
+        # The low-order bit set on the final octet promises another octet, and
+        # the warning names the bit that is set rather than one that is not
+        # (#2295). ``0x91`` is 145.
+        with self.assertWarns(ProtocolWarning) as caught:
             self.parse(header('8204ab91'))
+        self.assertEqual(str(caught.warning), 'IPv4: [OptNo 130] invalid format: '
+                                              'field termination indicator set on the final octet: 145')
 
     def test_timestamp_keeps_the_high_order_bit(self) -> None:
         from pcapkit.const.ipv4.option_number import OptionNumber
diff --git a/tests/protocols/internet/test_ipv4_unit.py b/tests/protocols/internet/test_ipv4_unit.py
index a57e1557d0..c9d2cc2eea 100644
--- a/tests/protocols/internet/test_ipv4_unit.py
+++ b/tests/protocols/internet/test_ipv4_unit.py
@@ -502,9 +502,9 @@ def test_ipv4_make_opt_sec_sets_the_field_termination_indicator(self) -> None:
         :rfc:`1108` section 2.4(a) makes the low-order bit of each protection
         authority octet a *field termination indicator*: ``1`` means another
         octet follows, ``0`` means this is the last. ``_read_opt_sec`` enforces
-        it, warning ``field termination indicator not set`` when the final octet
-        has it set. The writer and the reader agree with each other (#537) and
-        with the RFC (#1321).
+        it, warning ``field termination indicator set on the final octet`` when
+        the final octet has it set. The writer and the reader agree with each
+        other (#537) and with the RFC (#1321).
 
         The round trip is asserted through a real datagram and with warnings
         promoted to errors, because a disagreement's only symptom is a warning.